Here, we discuss briefly the origin of photons from DM annihilation (a very detailed discussion can be found in [1]}). Most of the photons are coming from pion decays; about 88-\(95\%\)  depending on the annihilation channel and on the DM mass. The contribution from \(\eta \)  decays is somewhat subleading which is about \(4\%\) . Finally, very sub-leading contributions are coming from bremsstrahlung photons and dominates in the high tail of the spectrum. Since the majority of photons (\(\simeq 95\%\) ) are coming from pion decays, the QCD uncertainties on photon spectra is strongly correlated to those on the pion spectra. We can distinguish between primary pions directly produced from QCD fragmentation and secondary pions coming from the decays of heavier hadrons and \(\tau \)  leptons. In all the final states [1]}, the number of secondary pions is larger than primary ones. The secondary pions account for about \(70\%\) -\(85\%\)  of the total pions. We note that the secondary pions mainly come from five sources: \(\rho ^\pm , \eta , \omega , D^{0,\pm }\)  and \(K_{S,L}\) .
